A newly modified dynamic aortic patch, a pneumatically powered in-series cardiac assist pump implanted in the descending thoracic aorta, will be studied in dogs in experimental chronic left ventricular failure. In matched dogs chronic LV failure (defined as steady-state mean left atrial pressure of greater than 20 mm Hg) will be induced by application of 50-microamperes anodal current to the intraluminal surface of selected left coronary artery branches for 24 hours; after 2-3 weeks, when the animal's cardiac condition has responded to opening of collateral vessels, additional coronary artery branches will be occluded as needed to produce stable failure. This may be repeated yet again. To quantitate the effects of DAP activation, a cross-over experimental design will provide for assisting one dog of a pair (Dog A) for 7 days while its control (Dog B) remains untreated; then assisting Dog B for a week while Dog A remains untreated; and repeating this sequence for a total of 12 cycles. Hemodynamic parameters will be recorded in both assisted and unassisted dogs during graded treadmill exercise; the animal's clinical condition will also be monitored. Each dog will be compared with its matched control dog and will serve as its own control. Left ventricular function curves will be constructed for all dogs coming to sacrifice. Hemostatic parameters will be monitored in vivo; post-sacrifice evaluations will include SEM and TEM assessment of the DAP and continguous tissues. The results will allow objective assessment of the hypothesis that modified DAP provides an effective treatment of chronic left ventricular failure.